The invention relates to a process for preparing epinastine hydrochloride in the high-melting crystal modification.
The compound epinastine (3-amino-9,13b-dihydro-1H-dibenz-[c,f]imidazolo[1,5-a]-azepine) belongs to the 2-aminoimidazolines and is a therapeutically active substances characterized primarily by its antiallergenic and antihistaminergic activity (EP 35749).
Methods of preparing epinastine hydrochloride are known from the prior art. In EP 35749, epinastine hydrochloride is obtained by precipitation from a methanolic solution with ether. DE 41 02 148 discloses the formation of epinastine hydrochloride by reaction of the free epinastine base with HCl in dimethyl formamide. The abovementioned processes for preparing epinastine hydrochloride which are known from the prior art do, however, have some disadvantages. Thus, epinastine hydrochloride cannot always be prepared in pure form using these methods or it is obtained in various crystal modifications. One known modification melts at about 250xc2x0 C. to 263xc2x0 C. (low-melting crystal modification) and another melts at about 275xc2x0 C. to 281xc2x0 C. (high-melting crystal modification). The use of alcohols in the precipitation of epinastine hydrochloride proposed in EP 35749 results in a loss of quality because of gradual decomposition of the product. In this process, the product also contains up to about 5% of the low-melting crystal modification, according to DSC (Differential Scanning Calorimetry). The process for preparing epinastine hydrochloride disclosed by DE 41 02 148 involves the use of dimethyl formamide, which can only be removed from the product of the process at high temperatures during drying, because of its high boiling point. As a result, the product begins to melt to some extert and changes color. In addition, drying on an industrial scale requires an unacceptably high energy consumption. Finally, dimethyl formamide has been classified as being damaging to the fetus, which means that its presence in a pharmaceutical composition has to be avoided at all costs.